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PHYSICS AND CHEMISTRY

Plato, Newton, Da Vinci, Goethe, Einstein: All these great minds and
many more grappled with the profound complexity of color. They sought to
understand it, creating systems to explain its mysterious workings.

Some fared better than others, and from the vantage point of our current
scientific knowledge, many of their attempts now seem funny, bizarre, or
downright fantastic. In the fifth century BC, Plato drew a causal
relationship between color vision and the tears in our eyes. The
eighteenth—and nineteenth-century philosopher Johann Wolfgang von
Goethe tried to impose order on color's chaos by arranging hues into
three groups: powerful, gentle/soft, and radiant/splendid. Although
we've come a long way in our understanding of color, much remains a
mystery.

Color is everywhere, but most of us never think to ask about its
origins. The average person has no idea why the sky is blue, the grass
green, the rose red. We take such things for granted. But the sky is not
blue, the grass is not green, the rose is not red. It has taken us
centuries to figure this out.

In a very dark chamber, at a round hole, about one-third part of an
inch broad, made in the shut of a window. I placed a glass prism,
whereby the beam of the Sun's light, which came in that hole, might be
refracted upwards toward the opposite wall of the chamber, and there
form a colored image of the sun.

—Sir Isaac Newton, Opticks

It stands to reason that for thousands of years, many casual observers
must have seen what Newton did: that light passing through a prism
creates a rainbow on the surface where it lands; but Newton saw
something no one else had seen. He deduced that the white light that
appears to surround us actually contains all the different colors we
find in a rainbow. White was not separate from these colors—or a
color unto itself—but was the result of all colors being reflected
at once. This counterintuitive and revolutionary theory did not take
hold easily. Some of those greatest minds we mentioned simply wouldn't
accept this theory. The idea that white light contained all color upset
Goethe so that he refused—and demanded others refuse—even to
attempt Newton's experiment.

NEWTON'S PRISM Although Newton's discovery was more than enough
to upset his contemporaries' digestion, he didn't stop there; Newton
also ascertained that colors refracted through a prism could not be
changed into other colors. Here's how he did it. He took a prism and
placed it between a beam of light (coming from the hole in his window
shutters) and a board with a small hole in it. The hole in the board was
small enough that it only allowed one of the refracted colors to pass
through it. He then placed all kinds of materials (including a second
prism) in front of the beam passing through the small hole to try to
alter the refracted color passing through the small hole. Prior to the
experiment, he had believed that if, for example, a blue piece of glass
was placed in front of a red beam of light, the red would be transformed
into another color. But he found that this was not the case. No matter
what color or type of material he placed in front of an individual beam
of light, he couldn't get the refracted color to change. From this
experiment, he deduced that there was a certain number of what he called
"spectral" colors—colors that cannot be broken down, colors that
are fundamental.

Once Newton confirmed that his spectral colors were unchangeable, he
decided to name them—and here's where his method takes a left turn
from the scientific to the fanciful. Taken with the idea that the
rainbow should reflect the musical scale, Newton decided to name his
colors in accordance with aesthetics. There are seven main tones in the
musical scale, so Newton came up with seven corresponding colors. Hence
the origin of ROYGBIV, the acronym by which we know Newton's seven
spectral colors—red, orange, yellow, green, blue, indigo, and
violet. Although the relationship to music was later set aside by
scientists who questioned the basis for comparison, ROYGBIV is still
used today as a teaching tool, even though indigo is not a color most
people can even identify.

The truth is, there's no perfect way to name the colors of the rainbow.
Take a look at a real rainbow (as opposed to a kindergartner's felt-tip
rendition), and you'll see that its colors merge seamlessly from one to
the other. Any judgment on where one color ends and the other begins is
arbitrary. Even Newton waffled on this point. At the beginning of his
experimentation, his spectrum included eleven colors. Once he'd whittled
the number down to seven, he still thought of orange and indigo as less
important, calling them semitones in another nod to the musical scale.

There's another issue with naming the colors of the rainbow: The
language of color is fluid, morphing over time and across geographies in
response to cultural forces that are sometimes too complex to pin down.
For example, the color Newton called indigo is the one most people would
identify as plain old blue or a true blue that falls midway between
green and violet. Newton's blue is what we now call cyan, a more
turquoise blue that falls between blue and green.

As for the name of the last color in the rainbow, why is it violet as
opposed to purple? Violet refers to the spectral color that looks bluish
purple. Purple refers not to a spectral color but to a color created by
a mix of light.

Color systems pre-and post-Newton have codified a whole host of
fundamental colors. By fundamental, we mean colors that our linguistic
or scientific models don't allow us to reduce any further. Today, if you
were asked to categorize the color navy, you would probably call it a
dark blue. If forced to generalize it even further, you would just say
it's a shade of blue, but there's nowhere to go from there. Throughout
history, our cultural understanding of fundamental colors has shifted
dramatically, ranging from the stark black and white model (where colors
were categorized merely by how dark or light they were) to systems made
up of dozens of colors, to systems in which some combination of red,
yellow, blue, green, and sometimes orange and violet/purple typically
reigns.

Today, we consider red, orange, yellow, green, blue, and violet as
fundamental. These fundamental colors are referred to as hues. Although
a color's value (put simply, how dark or light it is) and its chroma
(put simply, how dull or bright it is) can change, its hue is essential
to its identification.

Regardless of their number, the colors Newton called spectral should not
be confused with the colors we've been taught are the primary colors
that cannot be mixed and are therefore fundamental (i.e., red, blue, and
yellow) or the class of shades known as secondary colors (i.e. orange,
green, and purple). These secondary colors, we've been taught, result
from the mixing of the primary colors—red and yellow make orange,
red and blue make purple, and blue and yellow make green— and
therefore are not fundamental. But what Newton found was that orange,
green, and violet (which, to repeat, differs from purple) can be
spectral and just as fundamental as the colors we call primary. Orange,
for example, can result from a mix of light, but it can also be pure.
The same is true for red, blue, and yellow, even though we call them
"primaries." You can tell a color that is a mixture of light from a
spectral color by passing the light through a prism. The orange light
that is a mix will break into its components when passed through a
prism, but pure orange light will not.

Another major "aha moment" would soon follow for Newton: the discovery
that when red light was passed through a prism, it bent only slightly,
whereas violet light bent much more. This intriguing observation led
Newton to believe that each color was made up of unique essential
components. What made red red is different from what made violet violet.
Although he was on the right track, Newton incorrectly hypothesized that
light is composed of particles that travel in a straight line through
some kind of ether. What he called his "particle theory" was eventually
widely accepted.

Fast forward to the beginning of the nineteenth century, when an English
scientist named Thomas Young returned to a notion put forth by some of
Newton's contemporaries. Although Newton was convinced that light is a
particle, Young's experiments led him to believe that light—like
sound—is a wave. Another half-century later, the venerable James
Clerk Maxwell took Young's work and made a giant leap.

JAMES CLERK MAXWELL AND THE REIGN OF ELECTROMAGNETISM Before
James Clerk Maxwell's work, electricity and magnetism were believed to
be two separate forces, but Maxwell found the forces to be connected,
and he called this interconnection electromagnetism. Maxwell
showed how charged particles repel or attract one another, as well as
how these charged particles act like waves as they travel through space.

A particularly exciting part of Maxwell's treatise on the subject showed
that a specific group of electromagnetic waves is the cause of visible
light—in other words, the cause of color. He identified other
groups of electromagnetic waves, too, groups we now recognize as
ultraviolet light, radio waves, x-rays, and microwaves, to name a few.
All of these fall on the electromagnetic spectrum, and each is measured
and defined by its length and frequency, which are inversely
proportional. Every color has a different length and frequency, as does
every microwave, radio wave, or other wavelength on the electromagnetic
spectrum; but there is no essential quality separating visible light
from these other kinds of waves—except that our eyes (or to be
more precise, our brains) can perceive them as color.

To get a handle on exactly what length and frequency are all about,
imagine you are holding one end of a jump rope. Another person stands a
few feet away holding the other end. If you move your hand up and down
slowly, the movement will create one big arc—or wave—in the
center of the jump rope. Move your hand a little faster, and you will
get several waves occupying the same space as the single, big wave. Move
your hand faster still, and you will get many more waves that are even
closer together. The distance between the peak of one wave and the peak
of the next wave is the wavelength. The frequency is the number of waves
per second. As demonstrated via the jump rope, the smaller the
wavelength, the higher the frequency (or number) of waves.

Violet is the color with the shortest wavelength of visible light, at
380 to 450 nanometers (one nanometer is equal to one-billionth of a
meter), but the highest frequency at 789 to 668 THz (or terahertz, which
is the unit for frequency). On the spectrum of electromagnetic
radiation, it is the wave that is closest to ultraviolet and x-rays. Red
has the longest wavelength, at 620 to 740 nanometers, but the lowest
frequency of visible light is at 480 to 400 THz, closest to infrared and
microwaves.

Once Maxwell had shown visible light to be just one piece of the
electromagnetic puzzle, other pieces of the puzzle started falling into
place—or falling out of place. The scientist Max Planck remained
dissatisfied by Maxwell's theory that light was just a wave. His
experiments pointed to another dimension of light that he couldn't quite
put his finger on. Enter Albert Einstein, who took the reins and
eventually settled on the idea that light is indeed not just a wave, but
also a particle.

The fact that light can act at times like waves and at times like
particles—a phenomenon called the wave-particle duality of
nature—defies common sense, but it is the best explanation
scientists have found. The wave-particle duality of nature led to
quantum mechanics, which of all the branches of physics has arguably
had, directly or indirectly, the most influence on our current
understanding of the origins and workings of the universe.

THE REAL PRIMARY COLORS In addition to determining the physical
properties of color, scientists began to ask questions about our
perception of color. Why and how do we see color? The answers to these
questions lead us down a path that will counter almost everything you've
ever learned about color. Take the "white" light Newton was passing
through his prism. Newton's conclusion was that all the colors of the
rainbow combined to create white. But if you mix red, orange, yellow,
green, blue, and violet paint in your palette, you get anything but
white. (This, by the way, was the source of Goethe's extreme skepticism
about Newton's theories—he had watched painters mix paint in their
palettes and had never seen a multitude of colors add up to white.)

Newton was not dealing with paint, however; he was dealing with light,
and light mixes in an entirely different fashion. The mixing of light
belongs to the realm of additive color. When you add different
wavelengths of light together, you don't get the muddy mess you see with
paint and the mix doesn't always produce what you'd expect it to
because, again, additive color doesn't work like paint. In fact, every
color of the rainbow can be achieved by mixing only three colors of
light: red, green and blue. Wait, green?

That's a different triad from the primary colors—the colors from
which all others can theoretically be mixed—that we are taught
about in school, namely, red, blue, and yellow. Where did green come
from? And where did yellow go? These three new primary colors—red,
green, and blue—make no sense from a young painter's perspective.
Anyone who has ever mixed paint knows that you can't make yellow from
any of these colors. Yet, when you mix what appears to our human eyes as
red and green light, you do indeed get yellow.

You are probably more familiar than you think with this primary triad.
Case in point: the RGB (red, green, blue) color model on your computer
monitor. Obviously you see a wide range of colors on your screen, but if
you got close to an old computer with visible pixils, you could actually
see that the screen is entirely made up of red, green, and blue dots.
The same is still true today; the dots are just harder to see. If you
took a magnifying glass to your screen, you'd see that magenta type, a
field of pumpkins, and a dull brown bunny were all composed of these
red, green, and blue dots. A white screen is the result of all three
colors lighting up at the same maximum intensity, and a black screen is
the result of the absence of color.

Televisions and cameras also use an RGB color model, as does theater
lighting. Similarly, the first color photography (a feat conducted by
none other than James Clerk Maxwell in 1861) was a product of the
layering of red-filtered, green-filtered, and blue-filtered negatives on
top of one another. Here again, you can see the logical underpinnings of
the term additive color whereby adding colors together can beget every
color of the rainbow.

Why just red, green, and blue? What was the significance of these three
colors? At the beginning of the nineteenth century, Thomas Young (the
physicist who came up with the wave theory of light) wanted to find out.
His answer would come from a study of the human eye.

YOUR BRAIN ON COLOR If there's one color-related axiom that bears
repeating, it is this: Wavelengths of light do not exist as color until
we see them. Without the eyes and brain, there's no such thing as color.
Light waves are colorless until the moment they hit our eyes, at which
point our brains declare, "Blue sky, green grass, red rose!" Most other
animals—and even some humans—won't see any of these colors
when they look at the sky, the grass, or a rose because, again, none of
these entities is intrinsically colored.